Medical devices

ABSTRACT

Medical systems and methods including balloons having nanotubes are disclosed. In some embodiments, a medical system includes an elongated shaft, and an expandable balloon carried by the shaft and including nanotubes. The medical system is capable of cooling the balloon to less than about 37° C. In some embodiments, a method includes providing a medical device having an elongated shaft, and an expandable balloon carried by the elongated shaft and including nanotubes; and cooling the balloon to less than about 37° C.

RELATED APPLICATIONS

This application is a is a continuation of U.S. application Ser. No.12/838,980, filed Jul. 19, 2010, now U.S. Pat. No. ______, which is acontinuation of U.S. application Ser. No. 10/850,087, filed May 20,2004, now U.S. Pat. No. 7,758,572, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The invention relates to medical devices.

BACKGROUND

The body includes various passageways such as arteries, other bloodvessels, and other body lumens. These passageways, such as a coronaryartery, sometimes become constricted or blocked, for example, by plaqueor by a tumor. When this occurs, the constricted passageway can bewidened in an angioplasty procedure using a balloon catheter, whichincludes a medical balloon carried by a catheter shaft.

In an angioplasty procedure, the balloon catheter can be used to treat astenosis, or a narrowing of the body vessel, by collapsing the balloonand delivering it to a region of the vessel that has been narrowed tosuch a degree that fluid (e.g., blood) flow is restricted. The ballooncan be delivered to a target site by passing the catheter shaft over anemplaced guidewire and advancing the catheter to the site. In somecases, the path to the site can be rather tortuous and/or narrow. Uponreaching the site, the balloon is then expanded, e.g., by injecting afluid into the interior of the balloon. Expanding the balloon can expandthe stenosis radially so that the vessel can permit an acceptable rateof fluid flow. After use, the balloon is collapsed, and the catheter iswithdrawn.

In some cases, re-stenosis, which is the re-narrowing of the vessel, canoccur after an angioplasty procedure. To reduce the occurrence ofre-stenosis, the treatment site can be treated with, for example,prolonged balloon inflation, a heated balloon, a cooled balloon,radiation, drugs, and/or a stent.

SUMMARY

In one aspect, the invention features medical devices, such as cryogenicballoon catheters or heating balloon catheters, including nanotubes,such as carbon nanotubes. The nanotubes are capable of enhancing thethermal conductivity of the medical devices. In some embodiments, thenanotubes are incorporated in a polymer matrix, e.g., to form acomposite, and the nanotubes can enhance the mechanical properties ofthe composite. Thus, the medical devices are capable of providing goodheat transfer and good flexibility, which facilitates navigating thedevices through the body.

In another aspect, the invention features a medical system, including anelongated shaft and an expandable balloon carried by the shaft, theballoon having nanotubes, wherein the medical system is capable ofcooling the balloon to less than about 37° C.

In another aspect, the invention features a medical system, including anelongated shaft and an expandable balloon carried by the shaft, theballoon having nanotubes, wherein the medical system is capable ofheating the balloon to greater than about 37° C.

In another aspect, the invention features a method, including providinga medical device having an elongated shaft and an expandable ballooncarried by the elongated shaft, the balloon having nanotubes, andcooling the balloon to less than about 37° C. The method can includecooling the balloon to less than about 0° C. The method can furtherinclude contacting the balloon to a body vessel.

In another aspect, the invention features a method, including providinga medical device having an elongated shaft and an expandable ballooncarried by the elongated shaft, the balloon having nanotubes, andheating the balloon to greater than about 37° C.

In another aspect, the invention features a medical device, including anelongated flexible shaft for delivery into a body lumen, and a tissueheater at a distal portion of the shaft, the heater including nanotubes.The heater can be capable of being heated resistively. The device canfurther include a fluid supply capable of heating the heater with afluid at greater than about 37° C.

In another aspect, the invention features a medical device, including anelongated flexible shaft for delivery into a body lumen, the shafthaving a portion including nanotubes, and a fluid supply capable ofcooling the portion of the shaft with a fluid at less than about 37° C.The portion can be a distal portion.

Embodiments of the aspects may include one or more of the followingfeatures. The nanotubes include carbon nanotubes, such as single walledcarbon nanotubes. The balloon includes a blend comprising a polymer andthe nanotubes, such as from about 1% to about 50% by weight of thenanotubes. The nanotubes are functionalized. The nanotubes are aligned,e.g., by a magnetic field. The nanotubes are crosslinked. The nanotubesextend from an inner surface of the balloon and/or from an outer surfaceof the balloon. The system is capable of cooling or cooling an interiorsurface of the balloon and/or an exterior surface of the balloon. Thesystem further includes a second expandable balloon surrounding theexpandable balloon.

In another aspect, the invention features a medical device including acatheter having a distal end and a proximal end, a balloon at the distalend and having nanotubes, a heating source or a cooling source at theproximal end, and a conductor for carrying heat or cold from the heatingsource or the cooling source to the balloon.

Embodiments may have one or more of the following advantages. Treatingthe treatment site with heat and/or cold can reduce the occurrence ofrestenosis, particularly where use of a stent is not practical, such asin peripheral applications. Since thermal transfer is enhanced, thetreatment site can be cooled and heated more quickly, thereby reducingthe treatment time and/or adverse effect from a prolonged medicalprocedure. In some embodiments, the nanotubes can enhance the physicalproperties, e.g., strength, of the devices.

Other aspects, features, and advantages of the invention will beapparent from the description of the preferred embodiments thereof andfrom the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of a balloon catheter system including alongitudinal cross-section of a portion of a balloon catheter;

FIG. 2 is a cross-sectional view of the balloon catheter of FIG. 1,taken along line 2-2;

FIG. 3 is an illustration of a portion of the balloon catheter of FIG.1;

FIG. 4 is a flow chart of a method of a making a medical balloon;

FIG. 5 is an illustration of a substrate for making a medical balloon;

FIG. 6 is an illustration of an apparatus for making a medical balloon;

FIG. 7 is an illustration, along a longitudinal cross section, of aballoon catheter having an inner balloon and outer balloon;

FIG. 8 is an illustration, along a longitudinal cross section, of aballoon catheter having a proximal balloon and a distal balloon;

FIG. 9 is an illustration of a balloon catheter;

FIG. 10 is an illustration of a balloon catheter;

FIG. 11 is an illustration of a balloon catheter system including alongitudinal cross section of a balloon catheter; and

FIG. 12 is an illustration of a probe along a longitudinal crosssection.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a balloon catheter system 15 includes aballoon catheter 20 having an elongated catheter shaft 22 constructedfor delivery into a body vessel, and an expandable balloon 24 carried bya distal portion of the catheter shaft. Catheter shaft 22 includes aguidewire lumen 26 for passing balloon catheter 20 over an emplacedguidewire 28. Catheter shaft 22 further includes an inflation lumen 30and an exhaust lumen 32, both of which are in fluid communication withthe interior of balloon 24. As shown, inflation lumen 30 is also influid communication with a fluid supply 34 and a cold fluid supply 36.Other balloon catheter systems are described, for example, in Wang, U.S.Pat. No. 5,915,969; Hamlin, U.S. Pat. No. 5,270,086; and Lennox U.S.Pat. No. 6,428,534. In some embodiments, for example, the catheter shaftcan include concentric lumens.

During use, fluid is introduced through inflation lumen 30 and into theinterior of balloon 24. For example, to widen an occluded treatment sitein a body vessel during an angioplasty procedure, balloon 24 can beexpanded at the site by introducing the fluid through inflation lumen 30into the balloon at a rate faster than the rate at which the fluid exitsthe balloon through exhaust lumen 32, thereby radially expanding thevessel until the balloon is fully expanded and a steady state flow ismaintained by a difference in pressure between fluid entering theballoon and fluid exiting the balloon. Prior to and/or subsequent toexpanding the body vessel, the occluded site can be treated with acooled balloon, e.g., to reduce the occurrence of restenosis. Cold fluidfrom cold fluid supply 36 can be delivered through inflation lumen 30 ata sufficient pressure to expand balloon 24 and to contact the coldballoon against the body vessel.

Referring further to FIG. 3, balloon 24 is constructed to enhance heattransfer between the fluid in the balloon and the body vessel. As shown,balloon 24 is formed of a mixture 37 including nanotubes 38, such ascarbon nanotubes, and a polymer 40. Polymer 40 serves as a matrixmaterial that provides balloon 24 with resiliency and flexibility sothat the balloon can be navigated through the tortuous path to thetreatment site, inflated and deflated. Nanotubes 38 provide mixture 37with good thermal conductivity, e.g., relative to polymer 40, withoutsubstantially adversely affecting flexibility. For example, in someembodiments, a mixture having a first polymer and single wall carbonnanotubes can have a thermal conductivity from about 70% to about 125%higher than the thermal conductivity of the first polymer, depending onthe temperature. As a result, heat transfer through balloon 24 isfacilitated. In a procedure in which cold fluid is introduced intoballoon 24, the treatment site can be cooled more quickly, whichconsequently reduces the time for the procedure and reduces any adverseeffect from a prolonged medical procedure. Furthermore, since thethermal conductivity of the balloon is increased, heat resistancethrough the balloon is reduced and the temperature to which the bodyvessel is exposed more closely matches the temperature of the cold fluidintroduced into the balloon. In comparison, where the thermalconductivity of the balloon is low, the temperature of the fluid mayneed to be adjusted to compensate for the high resistance to heattransfer through the relatively poorly conducting balloon and/or therelatively prolonged procedure.

Moreover, in addition to enhancing thermal conductivity, nanotubes 38can also enhance the physical properties, such as strength, toughness,elasticity, and/or durability, of polymer 40. As a result, balloon 24can be made with a thinner wall thickness, without compromising, forexample, burst strength and pinhole resistance. For example, in someembodiments, a nanotube-containing polymer composite can have anultimate strength about twice as high as the ultimate strength of thepure polymer. As a result, to maintain about the same ultimate strength,the thickness of a structure including the nanotube-containing polymercan be reduced by about 50% (e.g., reduced by less than about 40%, 30%,20%, or 10%) relative to the thickness of a structure including the purepolymer. The thermal resistance of the wall is reduced both byincreasing the thermal conductivity and by reducing the wall thickness.The reduced wall thickness, in turn, reduces the profile of the balloon,thereby increasing its flexibility to navigate a tortuous path andaccessibility to relatively narrow body vessels.

In some embodiments, the nanotubes are on or near the inner surfaceand/or the outer surface of the balloon to enhance thermal transfer. Forexample, the nanotubes can extend from a surface, and/or the nanotubescan be less than several (e.g., about one or less) nanotube thicknessfrom a surface. Across the cross-sectional thickness of the balloonwall, the nanotubes can be in close proximity (e.g., contacting)relative to each other. Certain nanotubes can span the thickness of theballoon wall.

Nanotubes 38 include particles having at least one dimension less thanabout 1000 nm. Examples of nanotubes include hollow carbon nanotubes,such as hollow single walled carbon nanotubes and hollow multiwalledcarbon nanotubes (sometimes called buckytubes); ceramic nanotubes suchas boron nitride nanotubes and aluminum nitride nanotubes; and metallicnanotubes such as gold nanotubes. Certain carbon nanotubes, for example,can conduct heat as good as or better than diamond, and can conductelectricity similar to metals. Carbon nanotubes are available from, forexample, Rice University, and Carbon Nanotechnologies Inc. (CNI)(Houston, Tex.). Synthesis of carbon nanotubes is described, forexample, in Bronikowski et al., J. Vac. Sci. Technol. A, 19(4),1800-1805 (2001); and Davis et al., Macromolecules 2004, 37, 154-160.Boron nitride nanotubes are available from The Australian NationalUniversity (Can berra, Australia). More than one type of nanotubes canbe included in mixture 37.

The physical dimensions of nanotubes 38 can be expressed as units oflength and/or as a length to width aspect ratio. Nanotubes 38 can havean average length of from about 0.1 micron to about 20 microns. Forexample, the length can be greater than or equal to about 0.1 micron,0.5 micron, 1 micron, 5 microns, 10 microns, or 15 microns; and/or lessthan or equal to about 20 microns, 15 microns, 10 microns, 5 microns, 1micron, or 0.5 micron.

Nanotubes 38 can have an average width or diameter of from about 0.5 nmto about 150 nm. For example, the width or diameter can be greater thanor equal to about 0.5 nm, 1 nm, 5 nm, 10 nm, 25 nm, 50 nm, 75 nm, 100nm, or 125 nm; and/or less than or equal to about 150 nm, 125 nm, 100nm, 75 nm, 50 nm, 25 nm, 10 nm, 5 nm, or 1 nm. Alternatively or inaddition, nanotubes 38 can be expressed as having a length to widthaspect ratio of from about 10:1 to about 50,000:1. The length to widthaspect ratio can be greater than or equal to about 10:1, 100:1, or1,000:1; 2,500:1; 5,000:1; 10,000:1; 20,000:1; 30,000:1; or 40,000:1;and/or less than or equal to about 50,000:1; 40,000:1; 30,000:1;20,000:1; 10,000:1; 5,000:1; 2,500:1; 1,000:1, or 100:1. The nanotubespreferably have long lengths and small diameters. In some embodiments,the length of the nanotubes is as long as or longer than the thicknessof the wall of the balloon.

The concentration of nanotubes 38 in mixture 37 can be a function of,for example, the specific composition of the nanotubes, the dimensionsof the nanotubes, the composition of polymer 40, and/or the targetedthermal conductivity. In some embodiments, mixture 37 includes fromabout 0.5% to about 50% by weight of nanotubes 38. For example, mixture37 can include, by weight, greater than or equal to about 0.5%, 1%, 5%,10%, 15%, 20%, 25%, 30%, 35%, 40%, or 45% of nanotubes; and/or less thanor equal to about 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or 1%of nanotubes.

In some embodiments, nanotubes 38 are modified to enhance interactionsamong the nanotubes and/or interactions between the nanotubes andpolymer 40. Nanotubes 38 can be chemically modified with one or morefunctional groups that increase interactions (e.g., compatibility) withpolymer 40. Functionalization of carbon nanotubes are described, forexample, in Bahr et al., J. Am. Chem. Soc. 2001, 123, 6536-6542, andU.S. Patent Application Publication 2003/0093107. Alternatively or inaddition, nanotubes 38 can be connected or crosslinked, for example, byirradiation. Irradiation of carbon nanotubes are described, for example,in Krasheninnikov et al., Phys. Rev. B 66, 245403 (2002); Krasheninnikovet al., Phys. Rev. B 65 (2002) 165423; and commonly assigned U.S.application Ser. No. 10/850,085, filed May 20, 2004.

Polymer 40 can include, for example, thermoplastics and thermosets.Examples of thermoplastics include polyolefins, polyamides, such asnylon 12, nylon 11, nylon 6/12, nylon 6, and nylon 66, polyesters (suchas polyethylene terephthalate (PET)), polyethers, polyurethanes,polyvinyls, polyacrylics, fluoropolymers, copolymers and blockcopolymers thereof, such as block copolymers of polyether and polyamide,e.g., Pebax®; and mixtures thereof. Examples of thermosets includeelastomers such as EPDM, epichlorohydrin, polyureas, nitrile butadieneelastomers, silicones, etc. Thermosets, such as expoxies andisocyanates, can also be used. Biocompatible thermosets may also beused, and these include, for example, biodegradable polycaprolactone,poly(dimethylsiloxane) containing polyurethanes and ureas, andpolysiloxanes. Ultraviolet curable polymers, such as polyimides, canalso be used. Other polymers are described in commonly assigned U.S.application Ser. No. 10/645,055, filed Aug. 21, 2003. Mixture 37 caninclude one or more polymers 40.

In addition to nanotubes 38 and polymer 40, mixture 37 can furtherinclude one or more additives that enhance formation of a composite. Forexample, mixture 37 can include one or more coupling or compatibilizingagents, dispersants, stabilizers, plasticizers, surfactants, and/orpigments that enhance interactions between the nanotubes and thepolymer. Examples of additive(s) are described in U.S. PatentApplication Publication 2003/0093107.

Mixture 37 can be formed by combining nanotubes 38, polymer 40, andoptionally, one or more additives, and processing the combination usingcomposite-forming techniques. Methods of making nanotube-containingmixtures are described, for example, in Biercuk, et al., Applied PhysicsLetters, 80, 2767 (2002). The combination can be blow molded, filmmolded, injection molded, and/or extruded. Examples of method of makingmedical tubing using composite-forming techniques are described in U.S.Patent Application Publication 2003/0093107. Methods of forming aballoon from a tube are described in, for example, commonly-assignedU.S. application Ser. No. 10/263,225, filed Oct. 2, 2002, and entitled“Medical Balloon”; Anderson, U.S. Pat. No. 6,120,364; Wang, U.S. Pat.No. 5,714,110; and Noddin, U.S. Pat. No. 4,963,313, all herebyincorporated by reference in their entirety. The balloon can be attachedto catheter shaft 22, for example, by laser bonding. Catheter shaft 22may also be any of the multilayer tubes described in commonly assignedU.S. application Ser. No. 10/645,014, filed Aug. 21, 2003. In someembodiments, catheter shaft 22 includes nanotubes.

In other embodiments, balloon 24 can be formed by depositing nanotubes38 on a substrate, and subsequently removing the substrate. Referring toFIG. 4, a method 44 of making balloon 24 includes providing a removablesubstrate in the shape of the balloon (step 46). For example, referringto FIG. 5, a substrate 48 can be formed by molding (e.g., injectionmolding) a degradable or dissolvable material, such as polyvinyl alcohol(PVOH), into the shape slightly smaller than balloon 24. As shown,substrate 48 has a longitudinal lumen 50 and an outer surface with ahelically extending groove 52. Lumen 50 allows a material, such as hotwater, to be flushed through substrate 48 to remove the substratematerial. As described below, groove 52 allows a reinforcement materialto extend around the balloon. Alternatively or in addition, the outersurface of substrate 48 can be textured (e.g., dimpled) or roughened toincrease the surface area available for the nanotubes to be deposited.Degradable polyvinyl alcohol is described, for example, in Cooper etal., Proceedings of the 8^(th) Annual Global Plastics EnvironmentalConference, Society of Plastics Engineers, Detroit Mich., 360, 14 Feb.2002. In some embodiments, the substrate material, such as PVOH,includes nanotubes, for example, about 0.5% to about 70%, e.g., about0.5-50%, or 0.5-10%, of nanotubes by weight.

Referring again to FIG. 4, next, a layer containing nanotubes 48 isformed on substrate 48 (step 54). Nanotubes 48 can be dispersed in amixture, such as 1,1,2,2-tetrachioroethane (available from Zyvex) andpolyurethane (available from Estane).

Nanotubes 38 can be deposited on substrate 48 by spraying the nanotubemixture onto the substrate or by dip coating the substrate into themixture to form a first coating on the substrate. In some embodiments, amixture containing nanotubes 38 and 1,1,2,2-tetrachloroethane is appliedto substrate 48 first, followed by application of the mixture containingthe nanotubes, 1,1,2,2-tetrachioroethane, and polyurethane. As a result,a layer of nanotubes, sometimes called bucky paper, can be formed as aninterior surface of the balloon to enhance thermal conductivity. Inother embodiments, nanotubes 38 can be mixed with a UV crosslinkablepolymer, such as a polyimide or a polyester, as described in Meador, “UVCurable Polymers”, New Directions in High Performance Polymers, HamptonVa., Apr. 26-27, 2001.

In some embodiments, while the mixture containing nanotubes 48 hassufficiently low viscosity, the mixture can be magnetically processed toalign the nanotubes, which can enhance the thermal conductivity of themixture. The nanotubes can be aligned or oriented due to the cooperativeeffect of the magnetic torque exerted by the magnetic field on thenanotubes and by the hydrodynamic torque and viscous shear exerted onthe nanotubes by the polymer chains, which also respond to the field dueto magnetic anisotropy, as described in Choi et ah, J. of Appl. Phys.,Vol. 94, No. 9, 1 Nov. 2003, 6034-6039. The nanotubes can be aligned,for example, by exposing them to up to 25 Tesla for about two to fourhours at 25-60° C., as described in Choi et al.

In embodiments in which substrate 48 includes nanotubes, an outerportion or layer of the substrate can be removed prior to forming thefirst coating on the substrate. For example, hot water can be used toremove a layer of PVOH to expose the nanotubes. The exposed nanotubes,which may randomly protrude radially from the substrate, can bond wellwith the first coating. In addition, when the substrate is completelyremoved (described below), the nanotubes are partially embedded in theballoon and partially exposed at the surface of the balloon, whichprovides a highly thermally conductive inner layer for the balloon.

Alternatively or in addition, the balloon can be formed to include anouter layer having protruded or exposed nanotubes, as described below.

To strengthen the first coating, a reinforcement layer can optionally beformed on the first coating (step 56). For example, fibers of stainlesssteel, carbon, or Kevlar™ can be wrapped around substrate 48 alonggroove 52. Alternatively or in addition, fibers containing nanotubes canbe wrapped around the first coating. The fibers allow high loading(e.g., up to about 50% by weight) of nanotubes on the balloon.Nanotube-containing fibers can be formed, for example, byelectrospinning, described in Ko et al., Adv. Mater. 2000, 15, No. 14,Jul. 17, 1161-1163; and “Carbon Nanotube Reinforced Carbon NanoComposite Fibrils By Electro-Spinning”, thesis by Ashraf Abd El-FattahAli, Drexel University, October 2002. Next, additional layer(s)including nanotubes 38 is formed by applying one or more applications ofthe nanotube mixture (step 58) until the desired thickness is achieved.To form an outer layer having nanotubes that are partially exposed andpartially embedded in the balloon, a mixture containing PVOH andnanotubes can be sprayed onto a layer 38 before the layer has solidifiedto embed the nanotubes in the layer. Subsequently, the PVOH can beremoved, e.g., with hot water.

Substrate 48 can be removed by flushing lumen 50 with the appropriatematerial, such as hot water (step 60), thereby leaving a balloonincluding nanotubes. Embodiments of the method described above are alsodescribed in U.S. application Ser. No. 10/622,621, entitled “MedicalDevices and Processes for Preparing Same”.

Other methods of forming the balloon include forming a multilayerstructure having a plurality of alternating, oppositely charged layers,as described in U.S. application Ser. No. 10/849,742, entitled “MedicalDevices Having Multiple Layers” and filed May 20, 2004. The structurecan include, for example, a plurality of layers containing chargednanoparticles alternating with a plurality of layers containing chargedpoly electrolytes. Charging can be provided, for example, using anelectrical potential, by covalently attaching functional groups, and/orby exposing the layers to one or more charged amphiphilic substances.Exemplary materials and techniques are described in U.S. applicationSer. No. 10/849,742.

In other embodiments, a layer containing nanotubes can be formed byfiltering a mixture containing the nanotubes through an appropriatelyshaped filter. Referring to FIG. 6, a filter 61 generally having theshape of a balloon and a shape constraint 65 (such as a mesh form) areplaced in a vacuum chamber 63. Shape constraint 65 helps filter 61 tomaintain its shape under vacuum. A mixture 67 containing nanotubes (suchas the 1,1,2,2-tetrachloroethane mixture described above) is thenintroduced into filter 61, which is under vacuum. As a result, mixture67 is filtered through filter 61 (arrows), thereby leaving a layer ofnanotubes against the interior wall of the filter. One or moreadditional layers of nanotubes and/or polymer can be formed on the firstlayer of nanotubes; and/or the first layer of nanotubes can bereinforced as described above, in any combination. Filter 61 can beremoved to provide the finished balloon. In other embodiments, a mixturecontaining nanotubes can be injected or sprayed under pressure againstthe wall of a balloon-shaped filter.

Referring again to FIG. 1, in use, balloon catheter 20 can be deliveredto the treatment site by passing guidewire lumen 26 over an emplacedguidewire 28, and pushing the catheter to the treatment site. Thetreatment site can then be radially expanded by introducing fluid fromfluid supply 34, through inflation lumen 30, and into the interior ofballoon 24. Thereafter, the fluid can be removed through exhaust lumen32 to deflate balloon 24.

Prior to and/or subsequent to radially expanding the treatment site, acryogenic fluid (such as a liquid (e.g., cooled saline) or liquid/gasmixture including carbon dioxide or nitrous oxide) is introduced fromcold fluid supply 36, through inflation lumen 30, and into the interiorof balloon 24. The cryogenic fluid radially expands balloon 24 andcontacts the cooled balloon against the body vessel, thereby cooling thevessel. In other embodiments, the cryogenic fluid can be used toradially expand and to cool the body vessel simultaneously in one step.Methods of cryogenically treating a body vessel are described in Joye etal., U.S. Pat. No. 6,428,534, and Joye et al., U.S. Patent ApplicationPublication No. 2002/0045894.

In other embodiments, balloons of other balloon catheter systems can beformed to include nanotubes 38. Referring to FIG. 7, a balloon catheter70 includes an inner balloon 72 and an outer balloon 74 over the innerballoon. Inner balloon 72 can be used for cryogenic treatment, and outerballoon 74 can be used for vessel dilation, as well to reduce leakage ofcryogenic fluid into the body in case of inner balloon failure. Eitherballoon 72 or 74, or both balloons, can include nanotubes as describedabove. Embodiments of balloon catheter 70 and methods of using theballoon catheter are described in U.S. Patent Application PublicationNo. 2002/0045894.

Referring to FIG. 8, a balloon catheter 80 includes a distal balloon 82and a proximal balloon 84, both carried by a catheter shaft 86. Distalballoon 82 can be used for vessel dilation, and proximal balloon 84 canbe used for cryogenic treatment. Balloons 82 and 84 can be formed of thesame composition or of different compositions, e.g., the distal ballooncan include a compliant material, while the proximal balloon can includea non-compliant material. Either balloon 82 or 84, or both balloons caninclude nanotubes as described above. Embodiments of balloon catheter 80and methods of using the balloon catheter are described in U.S. Pat. No.6,428,534.

In some embodiments, nanotube-containing fibers, for example, made byelectrospinning, can be placed on a medical balloon to enhance thermalconductivity. The balloon can be a conventional balloon or the ballooncan include nanofibers as described above. The fibers can be wrapped,e.g., helically, about the balloon, and/or referring to FIG. 9, thefibers 90 can extend longitudinally along the length of the balloon 92.As shown in FIG. 9, the proximal ends of fibers 90 are connected to ahypotube 94, such as a metal wire insulated by a polymer. The proximalend of hypotube 94 can be submerged into a cryogenic fluid, such asliquid nitrogen, to further cool fibers 90 through conduction. As shown,fibers 90 are covered by polymer insulation 96 to reduce heat loss fromhypotube 94 to portions of the fibers 90 on balloon 92.

In other embodiments, referring to FIG. 10, fibers 90 can be in fluidcommunication with two hypotubes 94 and 140, and a reservoir 142. Asshown, a balloon catheter 144 includes hypotubes 94 and 140 that are influid communication with reservoir 142 (e.g., an annular chamber thatfits around the catheter shaft). Reservoir 142 is, in turn, in fluidcommunication with fibers 90. During use, fluid (e.g., a coolant) ispassed through a first hypotube (e.g., hypotube 94), to reservoir 142which distributes the fluid to fibers 90, and then passed through asecond hypotube (e.g., hypotube 140). The fluid exiting proximally fromthe second hypotube can be cooled and recirculated back to the firsthypotube, e.g., to form a closed loop of fluid flow. As shown, fibers 90extend generally longitudinally along the balloon. Alternatively or inaddition, fibers 90 can extend in other ways, such as helically.

The nanotube-containing balloons and the nanotube-containing mixturesdescribed above can also be used in heating or hyperthermic medicaldevices.

Referring to FIG. 11, a balloon catheter 100 includes a catheter shaft102 and a balloon 104 carried by the catheter shaft. Balloon catheter100 further includes two annular electrical contacts 106 and 108 carriedby shaft 102. Contacts 106 and 108 are connected to wires 110, whichextend proximally within shaft 102 to a power supply 112. Power supply112 is capable of flowing current between contacts 106 and 108, whichconsequently can heat inflation fluid in balloon 104. Balloon 104 and/orballoon catheter 100 can be formed according to any of the embodimentsdescribed above. As a result, the heat generated can be effectivelytransferred to a treatment site. The hyperthermal treatment can be used,e.g., to treat tumors, or to glaze or to smooth plaque from a vesselwall (e.g., by dehydration and compression), thereby enhancing vesselpatency. Embodiments of balloon catheter 100 and methods of using theballoon catheter are described in Lennox et al., U.S. Pat. No.4,955,377.

In some embodiments, the nanotubes can be incorporated only in selectedportion(s) of a cooling balloon or a heating balloon. For example, thenanotubes can be incorporated only in the inflatable, tissue-contactingbody portion of a balloon, but not in the tapered, conical regions orthe sleeve regions that connect to the catheter shaft.

Nanotube-containing mixture 37 described above can be applied to medicaldevices capable of heating tissue, e.g., to induce coagulation.Referring to FIG. 12, a radiofrequency (RF) probe 110 includes a shaft112 having an RF tip 114. Tip 114 includes an electrode portion 116, anda thermistor assembly 118 embedded in the electrode portion. Thermistorassembly 118, which is connected to a pair of leads 120, is capable ofsensing the temperature of electrode portion 116 as an indirectindication of the temperature of tissue surrounding the electrode. Asingle RF electrode lead 122 connects with electrode portion 116 atresistance weld 124. During use, an RF electrical current is appliedfrom probe 110 to pass through body tissue to locally heat the tissue.In preferred embodiments, electrode portion 116 includes (e.g., isformed of) nanotube-containing mixture 37 described above to enhanceheat transfer and electrical conductance between probe 110 andsurrounding tissue.

In addition, since heat resistance through electrode portion 116 isrelatively low, the temperature sensed by thermistor assembly 118 moreaccurately indicates the temperature of the surrounding tissue, e.g.,relative to other nonmetallic materials. The relatively soft tipprovided by mixture 37 can also reduce the occurrence of injury from arelatively harder tip. Embodiments of heating devices, such as RFprobes, guidewire probes, forceps devices, and catheters, methods ofusing the heating devices are described in Lennox, et al., U.S. Pat. No.5,122,137.

Still other hypothermic and hyperthermic devices can include nanotubesfor enhanced thermal conductivity. Examples of such devices include acatheter shaft having, at the distal portion of the shaft, a heatableelement and/or a structure that can be cooled or heated, as described,for example, in Ginsburg, U.S. Pat. No. 5,486,208. The distal portion ofthe catheter shaft can be formed of a composite including a polymer andnanotubes for good thermal conductivity.

The following example is illustrative and not intended to be limiting.

Example

This example describes a method of making a tube including a compositeof carbon nanotubes and a polymer. The polymer was PEBAX 7233 fromAtoFina, Philadelphia, Pa. and the carbon nanotubes were MB4220, a PA 12based carbon nanotube master batch from Hyperion CatalysisInternational, Cambridge, Mass. The carbon nanotube content was 20%. ThePEBAX 7233 polymer and the MB4220 nanotubes were hand mixed at 3:1 ratioby weight, respectively.

Next, the materials were compounded. The compounding equipment includeda ThermoHaake Polylab system, which includes an instrumented drivesystem, a 16 mm co-rotating twin screw extruder, and downstreamquenching and pelletizing equipment. Pellets were fed into the extruderusing a Ktron loss in weight feeder. The aggressive mixing screw wasused in the compounding process. The mixture was fed at 24 g/minute. Thescrew speed was 250 rpm. The melt temperature was about 237° C.

These compounded pellets were used for tubing extrusion. The tubing sizewas 0.0355 I.D.×0.0605 O.D. A 0.75-inch Brabender extruder was used fortubing extrusion. The barrel temperatures were 360/385/400F and the dietemperature was 410F. The extrusion line was equipped with 0.16 cc-meltpump at 45 rpm and 55 microns melt filter. The area draw down ratio was8.68. All publications, applications, patents, and references referredto in this application are herein incorporated by reference in theirentirety. Other embodiments are within the claims.

What is claimed is:
 1. A balloon catheter, comprising: a first elongateshaft having a proximal end and a distal end; an expandable balloonaffixed to the first elongate shaft adjacent the distal end thereof; anda first and second annular electrical contacts carried by the firstelongate shaft, the electrical contacts positioned adjacent to thedistal end of the first elongate shaft and within the expandableballoon; wherein the expandable balloon comprises a composite materialincluding at least one polymer and a plurality of carbon nanotubes. 2.The balloon catheter of claim 1, wherein the first and second electrodesare configured to heat an inflation fluid disposed within the expandableballoon.
 3. The balloon catheter of claim 1, wherein at least some ofthe plurality of carbon nanotubes extend from an inner surface of theexpandable balloon to an outer surface of the expandable balloon.
 4. Theballoon catheter of claim 1, wherein the composite material has athermal conductivity in the range of 70 percent to 125 percent higherthan the thermal conductivity of the at least one polymer.
 5. Theballoon catheter of claim 1, further comprising at least one fiberhaving a proximal end and a distal end, the at least one fiber extendingalong an outer surface of the expandable balloon.
 6. The ballooncatheter of claim 5, wherein the at least one fiber extendslongitudinally along the outer surface of the expandable balloon.
 7. Theballoon catheter of claim 5, wherein the at least one fiber is helicallywrapped around an outer surface of the expandable balloon.
 8. Theballoon catheter of claim 5, wherein the at least one fiber includesnanoparticles.
 9. The balloon catheter of claim 5, further comprising asecond elongate shaft extending along the first elongate shaft.
 10. Theballoon catheter of claim 9, wherein the proximal end of the at leastone fiber is attached to a distal end of the second elongate shaft. 11.The balloon catheter of claim 10, wherein the second elongate shaft isconfigured to heat the at least one fiber through conduction.
 12. Aballoon catheter, comprising: a first elongate shaft having a proximalend and a distal end; an inflatable balloon affixed to the firstelongate shaft adjacent the distal end thereof, the balloon comprising acomposite material including a least one polymer and a plurality ofcarbon nanotubes, and the composite material has a thermal conductivityin the range of 70 percent to 125 percent higher than the thermalconductivity of the at least one polymer; a first and second annularelectrical contacts carried by the first elongate shaft, the electricalcontacts positioned adjacent to the distal end of the first elongateshaft and within the balloon; and a power supply positioned adjacent theproximal end of the first elongate shaft and in electrical communicationwith the first and second electrical contacts; wherein the power supplyflows current between the first and second electrical contacts to heatan inflation fluid disposed within the balloon.
 13. The balloon catheterof claim 12, wherein at least some of the plurality of carbon nanotubesextend from an inner surface of the expandable balloon to an outersurface of the balloon.
 14. The balloon catheter of claim 12, furthercomprising at least one fiber having a proximal end and a distal end,the at least one fiber extending along an outer surface of the balloon.15. The balloon catheter of claim 14, wherein the at least one fiberextends longitudinally along the outer surface of the balloon.
 16. Theballoon catheter of claim 14, wherein the at least one fiber ishelically wrapped around an outer surface of the expandable balloon. 17.The balloon catheter of claim 14, wherein the at least one fiberincludes nanoparticles.
 18. A balloon catheter, comprising: an elongatemember having a proximal end and a distal end; an expandable balloonattached to the elongate member adjacent the distal end thereof; two ormore electrical contacts carried by the elongate shaft, the electricalcontacts positioned adjacent to the distal end of the elongate shaft andwithin the expandable balloon; a power supply positioned adjacent theproximal end of the first elongate shaft and in electrical communicationwith the first and second electrical contacts; and one or more fiberseach having a proximal end and a distal end, the one or more fibersextending along an outer surface of the balloon; wherein the powersupply flows current between the first and second electrical contacts toheat an inflation fluid disposed within the balloon.
 19. The ballooncatheter of claim 18, wherein the one or more fibers includenanoparticles.
 20. The balloon catheter of claim 18, wherein theexpandable balloon includes nanoparticles.